Conventional liquid-filled electric radiant heaters, such as electric oil-filled heaters, provide a portable means for producing heat. Generally, in an oil-filled heater, oil flows through a set of radiating elements or fins, and is heated when it comes into contact with a heating element.
Oil-filled heaters are formed from a plurality of metal, rectangular-shaped chambers, known as fins. Each fin is provided with a cavity to accommodate or contain the oil. With the exception of the rear end fin, each fin has two openings on each side of the fin which align with corresponding openings in adjacent fins. The rear end fin has one side with no openings, as this side of the fin is typically exposed (i.e., is not covered by a shroud). The fins are welded together around the openings, providing a path within the heater through which the oil may flow. After the fins are welded together, the openings of the front end fin remains unsealed. These openings of the front end fin provide for insertion and attachment of the heating element and the filling of the oil medium. The heater may be painted after the outer fins are sealed onto the fin assembly and after one of the front end openings is sealed. However, the heater must be filled with oil after the heater is subjected to the heat of conventional industry painting operations.
The prior art heater assemblies, as shown in FIGS. 5 and 6, include a closure for the openings of the front end fin. The bottom opening of the front end fin is sealed using a bottom end closure assembly, as shown in FIG. 6. The bottom end closure assembly includes a threaded inner nut 10, a threaded heating element 18 and a gasket 16.
The threaded inner nut 10 is inserted into the fin adjacent the bottom opening. The inner nut 10 must be inserted into the fin prior to sealing the fin halves together. The inner nuts 10 have legs 12 extending from the sides of the threaded portion 14 to place the threaded portion 14 in the proximity of the opening. Thus, once the inner nuts 10 are inserted into the fin and the fin is assembled, that fin must be oriented so that the threaded portion 14 faces the front end of the heater assembly.
The threaded heating element 18 is inserted into the front bottom opening and manually threaded onto the threaded inner nut 10. The gasket 16 is placed between the heating element 18 and the side of the fin to restrict oil leakage from within the heater. A wrench is used to apply rotational force of the heating element 18 to compress the gasket 16; thus, the heating element 18 typically has a hexagonal-shaped head.
The front top opening of prior art heaters is sealed using a top end closure assembly, as shown in FIG. 5. The top end closure assembly consists of a plate 20 which is welded onto the front top opening. In the alternative, a more common top end closure assembly resembles the bottom closure described above, as it includes a threaded inner plug, a threaded cover plate and a gasket. In the alternative embodiment, the threaded inner plug is inserted within the fin prior to assembly of the fin. The inner plug is placed adjacent the front top opening in a manner similar to that for the bottom end closure assembly described above. The threaded cover plate is then manually threaded into the top inner plug, with a gasket placed between the cover plate and the top inner plug to compress and thereby restrict oil leakage between the bolt and the top inner plug. The cover plate, like the heating element 18, generally has a hexagonal-shaped head for the same reasons stated above.
Generally, prior art heaters are filled by first sealing the top opening, as described above. Oil is then filled into the heater through the bottom opening, the heating element is inserted, and the bottom opening is sealed by compression of the gasket between the heater body and the heating element, as described above. In the alternative, the bottom opening may be sealed prior to filling the heater through the top opening, and the top opening may then be sealed by using a threaded cover plate.
One problem which arises with conventional oil-filled heaters is that the heaters tend to leak around the gaskets. This leakage is believed to be primarily caused by repeated heating and cooling of the gasket due to normal use of the heater. Also, the seal formed by the compression of the gasket may leak due to poor alignment of the heating element when threaded into the insert, or due to misalignment. The oil leak is unsightly, and creates a mess around the heater. In addition, leakage of oil results in loss of volume of oil within the heater and leads to a decrease or loss of oil circulation. If an insufficient amount of oil is circulating in the heater, the heater is inefficient, as the top of the fins are cold and the bottom of the fins overheat, resulting in discoloration of the fins.
Another problem prevalent in conventional oil-filled heaters is that the method of sealing the heaters is quite involved and complex and is inherently unreliable. Because the outer fin requires threaded inner plugs to be inserted prior to welding the fin halves together, the time and cost of manufacturing that end fin is higher. Further, because of the inserted threaded plug, the end fin is not interchangeable and all of the fins cannot be assembled using the same steps, as in an assembly line. Rather, the outer fins must be assembled using a different procedure so that the inner plugs are inserted prior to welding the fin halves together. Further, these end fins must be in the proper orientation when assembled to the other fins of the heater to ensure that the threaded portion can receive the bolt or heating element. Yet another problem with prior art heater assemblies is that the gasket seal is susceptible to leakage, and the threading is difficult to align.
Because the inner plugs are not secured to the fins, to ensure proper placement of the inner plug, the heating element and/or threaded plate must be manually threaded onto the heating assembly.